This invention relates to a control valve assembly and more particularly to an underwater connectory valve assembly for use in the exercise of remote control over subsea wellhead functions.
In subsea drilling operations, it is necessary to control and monitor the wellhead apparatus from the drilling rig. The remote control of subsea wellhead functions during drilling operations requires the use of a subsea hydraulic connector. Hydraulic supply pressure and command signals (electric or hydraulic) originate on the surface and are transmitted subsea via an umbilical link to the hydraulic connector. The hydraulic connector serves to selectively route the hydraulic supply to the appropriate wellhead component, thereby actuating the component per surface-initiated commands.
A typical subsea hydraulic connector assembly consists of three basic components: (1) a control module or pod which contains pilot-operated control valves and regulators, porting, seals, etc., for directing the hydraulic control signals as appropriate to exercise control over the various wellhead, i.e., stack functions; (2) an upper stack assembly mounted on a Blow-Out Preventor stack frame; and (3) a lower-marine riser package mounted on the upper portion of the wellhead. Generally, the control pods are independently retrievable for repair of the control valves, regulators, hose bundle, etc., since it is less costly to retrieve the pod than to retrieve the riser package and upper stack assembly.
In use, a control pod is lowered and locked to the subsea mandrel comprising the upper stack assembly or riser package. The pod generally contains resilient face-sealing elements which seal against the mandrel walls thereby providing remote make/break communication to the subsea wellhead components. These sealing elements may be of annular configuration to surround the individual outlet ports in the control pod. The control pod is keyed to the mandrels in such a manner as to align the individual pod outlet ports with the corresponding inlet ports of the mandrels when a pod is landed and locked to a mandrel.
Various pod-mandrel configurations have been utilized in an effort to prevent damage to the sealing elements as a pod is lowered onto a mandrel. One common method of reducing seal damage is to taper the pod/mandrel interface downwardly and inwardly to prevent the seals from dragging across the mandrel wall.
Another seal protection method utilizes a seal which is retracted during the mounting of the pods to the mandrels and extended for sealing engagement with the mandrel interface upon control actuation. Such an underwater connector is shown in LeMoine U.S. Pat. No. 4,404,989.
The use of retractable valve seals results in fluid loss through intermittent exhaust of the supply pressure to the interface vent space during both retraction and extension of the seal. That is, during extension of the seal toward the mandrel interface, the supply pressure is intermittently connected to the interface vent space causing fluid loss. Similarly, in retracting the seal from the mandrel interface, the supply pressure is again intermittently connected to the vent space resulting in a loss of fluid.